From d9a2c32acaa01922aa422308ebbaa147911c5d46 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 21 Jul 2017 18:21:12 -0400
Subject: [PATCH] Made an attempt to obey the proper TZX rules on gaps, and to
 hit the common-clock-rate `Time` optimisation.

---
 Storage/Tape/Formats/TZX.cpp | 47 ++++++++++++++++++++++++------------
 Storage/Tape/Formats/TZX.hpp |  5 +++-
 2 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/Storage/Tape/Formats/TZX.cpp b/Storage/Tape/Formats/TZX.cpp
index 6829b6c43..37b0cb169 100644
--- a/Storage/Tape/Formats/TZX.cpp
+++ b/Storage/Tape/Formats/TZX.cpp
@@ -12,11 +12,12 @@ using namespace Storage::Tape;
 
 namespace {
 const unsigned int StandardTZXClock = 3500000;
+const unsigned int TZXClockMSMultiplier = 3500;
 }
 
 TZX::TZX(const char *file_name) :
 	Storage::FileHolder(file_name),
-	next_is_high_(false) {
+	current_level_(false) {
 
 	// Check for signature followed by a 0x1a
 	char identifier[7];
@@ -37,16 +38,14 @@ TZX::TZX(const char *file_name) :
 
 void TZX::virtual_reset() {
 	clear();
+	set_is_at_end(false);
+	fseek(file_, 0x0a, SEEK_SET);
 
 	// This is a workaround for arguably dodgy ZX80/ZX81 TZXs; they launch straight
 	// into data but both machines require a gap before data begins. So impose
 	// an initial gap, in the form of a very long wave.
-	emplace_back(Tape::Pulse::Low, Storage::Time(1, 4));
-	emplace_back(Tape::Pulse::High, Storage::Time(1, 4));
-
-	set_is_at_end(false);
-	next_is_high_ = false;
-	fseek(file_, 0x0a, SEEK_SET);
+	current_level_ = false;
+	post_gap(500);
 }
 
 void TZX::get_next_pulses() {
@@ -95,7 +94,7 @@ void TZX::get_generalised_data_block() {
 
 	get_generalised_segment(total_pilot_symbols, maximum_pulses_per_pilot_symbol, symbols_in_pilot_table, false);
 	get_generalised_segment(total_data_symbols, maximum_pulses_per_data_symbol, symbols_in_data_table, true);
-	emplace_back(Tape::Pulse::Zero, Storage::Time((unsigned int)pause_after_block, 1000u));
+	post_gap(pause_after_block);
 
 	// This should be unnecessary, but intends to preserve sanity.
 	fseek(file_, endpoint, SEEK_SET);
@@ -146,9 +145,9 @@ void TZX::get_generalised_segment(uint32_t output_symbols, uint8_t max_pulses_pe
 			// Mutate initial output level.
 			switch(symbol.flags & 3) {
 				case 0: break;
-				case 1: next_is_high_ ^= true;	break;
-				case 2: next_is_high_ = false;	break;
-				case 3: next_is_high_ = true;	break;
+				case 1: current_level_ ^= true;	break;
+				case 2: current_level_ = true;	break;
+				case 3: current_level_ = false;	break;
 			}
 
 			// Output waves.
@@ -160,11 +159,6 @@ void TZX::get_generalised_segment(uint32_t output_symbols, uint8_t max_pulses_pe
 	}
 }
 
-void TZX::post_pulse(unsigned int length) {
-	emplace_back(next_is_high_ ? Tape::Pulse::Low : Tape::Pulse::High, Storage::Time(length, StandardTZXClock));
-	next_is_high_ ^= true;
-}
-
 void TZX::get_standard_speed_data_block() {
 	__unused uint16_t pause_after_block = fgetc16le();
 	uint16_t data_length = fgetc16le();
@@ -208,3 +202,24 @@ void TZX::get_pulse_sequence() {
 		post_pulse(fgetc16le());
 	}
 }
+
+#pragma mark - Output
+
+void TZX::post_pulse(unsigned int length) {
+	post_pulse(Storage::Time(length, StandardTZXClock));
+}
+
+void TZX::post_gap(unsigned int milliseconds) {
+	if(!milliseconds) return;
+	if(milliseconds > 1 && !current_level_) {
+		post_pulse(Storage::Time(TZXClockMSMultiplier, StandardTZXClock));
+		post_pulse(Storage::Time((milliseconds - 1u)*TZXClockMSMultiplier, StandardTZXClock));
+	} else {
+		post_pulse(Storage::Time(milliseconds*TZXClockMSMultiplier, StandardTZXClock));
+	}
+}
+
+void TZX::post_pulse(const Storage::Time &time) {
+	emplace_back(current_level_ ? Tape::Pulse::High : Tape::Pulse::Low, time);
+	current_level_ ^= true;
+}
diff --git a/Storage/Tape/Formats/TZX.hpp b/Storage/Tape/Formats/TZX.hpp
index e0eb6b432..d0a3eedfd 100644
--- a/Storage/Tape/Formats/TZX.hpp
+++ b/Storage/Tape/Formats/TZX.hpp
@@ -35,7 +35,7 @@ class TZX: public PulseQueuedTape, public Storage::FileHolder {
 		void virtual_reset();
 		void get_next_pulses();
 
-		bool next_is_high_;
+		bool current_level_;
 
 		void get_standard_speed_data_block();
 		void get_turbo_speed_data_block();
@@ -46,6 +46,9 @@ class TZX: public PulseQueuedTape, public Storage::FileHolder {
 		void get_generalised_segment(uint32_t output_symbols, uint8_t max_pulses_per_symbol, uint8_t number_of_symbols, bool is_data);
 
 		void post_pulse(unsigned int length);
+		void post_gap(unsigned int milliseconds);
+
+		void post_pulse(const Storage::Time &time);
 };
 
 }